1. Field of the Invention
This invention relates to an improved method of controlling the filter cake composition of a water-based drilling fluid by admixing colloidal solids with at least one carrier, whereby the colloidal solids are suspended in the carrier and then admixing polymeric beads to the suspension prior to adding the suspended mixture to the drilling fluid. More specifically, the present invention relates to a drilling fluid additive mixture manufactured by a method comprising of pre-wetting copolymer beads and talc with oils or glycols to form a suspended mixture and then adding the suspended mixture to the drilling fluid.
2. Description of the Related Art
New technology in drilling for oil and gas now includes horizontal drilling. The horizontal drilling concept exposes more surface area of the producing zone than the conventional vertical drilling operations. For example, if a producing zone is fifty feet in thickness and a vertical well is drilled through such a zone, then only fifty feet of the producing zone will be exposed for production. In contrast, a horizontally drilled well may penetrate the producing sand or zone by one thousand feet or more. The amount or volume of oil or gas production is directly proportional to the horizontal penetration in feet into the producing sand or zone. In horizontal or directional drilling where the drill pipe must bend in order to achieve the desired penetration into the producing zone, friction becomes a major problem. The primary source of friction is directly related to the adhesion of the drilling assembly to the wall cake which lines the drilled well bore. The capillary attractive forces generated by the adhesion of the drilling assembly to the wall cake are directly proportional to the amount or footage of the drilling assembly exposed to the surface of the wall cake.
In horizontal or directional wells, many methods have been used in order to reduce friction between the drilling assembly and the wall cake. One such method would be to add a liquid lubricant to the drilling fluid in order to reduce the coefficient of friction of the drilling fluid. These liquid lubricants include oils, such as hydrocarbon based oils, vegetable oils, glycols, etc. These liquid lubricants will usually reduce the coefficient of friction of the drilling fluid resulting in a reduction of friction between the drilling assembly and the wall cake of the well bore.
When the liquid lubricant is added to the drilling fluid, it has several options as to how it will react. One option is that the lubricant remains isolated and does not mix well with the drilling fluid. A second option is that the lubricant emulsifies with the water in the drilling fluid to form an oil-in-water emulsion. Still another option is the oil attaching itself to the commercial solids in the drilling fluid or to the drilled cuttings or drilled solids. In certain circumstances, some of the liquid lubricant might be deposited or smeared onto the wall cake of the well bore. The ideal scenario would be to have all of the liquid lubricant deposited on the wall cake.
Those experienced in drilling fluid engineering know that a thin, tough, pliable, and lubricious wall cake is most desirable. The integrity of a wall cake is determined by several factors. The thickness of a wall cake is directly proportional to the amount of liquid leaving the drilling fluid, and being forced into the wall of the well bore by hydrostatic pressure. The thickness of the wall cake is also determined by the type and particle size of the solids in the drilling fluid. Particle Size Distribution, or PSD is important to the wall cake integrity. Experts in drilling fluids also know that materials such as bentonite clay, starches, lignites and polymers are all used to build acceptable wall cakes. It is known in the prior art that various food grade vegetable oils are acceptable lubricants when used alone in water-based drilling fluids. It is also known in the prior art that round co-polymer beads when used alone in water-based drilling fluids function as a good friction reducer. However, much more is required to improve the wall cake integrity and lubricity of most well bores. In addition, there is no technology or process in the prior art that improves the lubrication or friction reducing capacity of the copolymer beads.
Furthermore, the solids control equipment used on the drilling rigs today is far superior as to what was used 15 to 20 years ago. In the past, drilling rig shale shakers would probably be limited to screen sizes of about 20-40 mesh on the shakers. These coarser mesh screens would allow pieces of shale and the drilled formation to pass through the shaker screens back into the drilling fluid and then recirculated back down the well bore. As these larger than colloidal size particles make their way back up the well bore to the surface, the action of the drilling assembly rotating within the well bore forces these larger particles into the surface of the well bore. For example: a 20xc3x9720 mesh shaker screen would allow a drilled cutting sized at 863 microns or 0.0340 inches to pass through it and then the cutting would be returned to the well bore and some of these 863 micron cuttings would eventually be embedded into the wall cake. This would give the wall cake surface a texture resembling that of coarse sandpaper. These larger particles would allow the drilling fluid to channel and pass between the drilling assembly and the wall cake thereby reducing the negative effect of the capillary attractive forces generated by the close contact of the drilling assembly with the wall cake. The instances of the drilling assembly becoming stuck to the wall cake when less efficient solids control equipment, such as shale shakers, was used much less than it is today. The more efficient shale shakers today are a great improvement for the drilling fluids but the instances of sticking the drilling assembly are higher. The reason for a higher rate of stuck drilling assemblies today could be blamed on cleaning the drilling fluid to efficiently. Today many drilling rigs utilize cascading shale shakers, which eventually pass the drilling fluid through 200 mesh or 74 micron screens. This is very positive for controlling the percentage of drilled solids in the drilling fluid but it also affects the texture or surface of the wall cake. The finer the solids on the surface of the wall cake are, the greater the capillary attractive forces will be between the drilling assembly and the wall cake.
The present invention provides a method of enhancing the surface of the wall cake. In order to accomplish this, the invention provides a method, which adds something to improve the texture of the surface of the wall cake, and then adds something to prevent large amounts of water from leaving the drilling fluid then passing through the wall cake into the formation. The present invention also provides a carrier for the colloidal solids and beads, which also acts as a lubricant for the drilling fluid. The present invention further provides a process that reduces the effect of capillary attractive forces between the drilling assembly and the wall cake, thereby reducing the tendency of the drilling assembly to become stuck. In high angle directional wells where down hole motors are used to rotate the drill bit and the drill pipe remains stationary, it is important that the drilling assembly can xe2x80x9cslidexe2x80x9d as the drilling bit cuts more holes. The resent invention improves the ability to xe2x80x9cslidexe2x80x9d while drilling as stated above.
In one embodiment, the present invention relates to a drilling fluid additive mixture manufactured by a method comprising of admixing colloidal solids with at least one carrier to create a suspended mixture, the solids having an affinity for oils, esters, glycols and olefins, and the suspended mixture allowing the surface of the solids to be pre-wet with the carrier prior to adding the mixture to a drilling fluid. In another embodiment, the drilling fluid additive mixture further comprises admixing copolymer beads to the suspended mixture. In still another embodiment, the solids have an affinity for oils, esters, glycols and olefins. The carrier of the present invention also functions as a lubricant.
In yet another embodiment, the beads have a specific gravity at from about 1.0 to about 1.5 and a size from about 40 microns to about 1500 microns. In still yet another embodiment, the beads are comprised of styrene and divinylbenzene. In a further embodiment, the solids have a size range from about 2 microns to about 40 microns. In still a further embodiment, the solids are comprised of talc. For purposes of this invention, talc is a mineral, which is magnesium silicate. Talc is extremely hydrophobic and thus, repels water. Since talc has excellent water repellant properties, it would be advantageous to have the surface of the walls of the base mud wall cake to be completely covered or coated with talc.
In yet a further embodiment, the carrier consists essentially of oils, hydrocarbon oils, vegetable oils, mineral oils, paraffin oils, esters, glycols, cellulose and olefins. In still yet a further embodiment, the carrier comprises soybean oil. In another further embodiment, the carrier may be esters, fatty acids and glycols such as poly propylene glycol. In a further embodiment, the carrier comprises oil and a glycol In yet a further embodiment, the carrier consists essentially of polyanionic cellulose, polyanionic cellulose polymer, and carboxymethylcellulose.
In still another further embodiment, the solids comprises from about 2% to about 50% of the additive mixture of the present invention. In yet another further embodiment, the carrier comprises from about 50% to about 98% of the additive mixture. In still yet another embodiment, the beads comprises from about 2% to about 50% of the additive mixture.
In another embodiment, the present invention relates to a method of manufacturing a drilling fluid additive mixture, the method comprises: shearing colloidal solids with at least one carrier to create a suspended mixture to thereby allow the surface of the solids to be pre-wet with the carrier; and admixing copolymer beads to the suspended mixture. In yet another embodiment, the solids and the beads having an affinity for oils, esters, glycols and olefins. In another embodiment, the beads are sheared with the suspended mixture until a homogeneous mixture is formed.
In still yet another embodiment, the beads have a specific gravity at from about 1.0 to about 1.5 and a size from about 40 microns to about 1500 microns. In a further embodiment, the beads are comprised of styrene and divinylbenzene. In yet a further embodiment, the solids have a size range from about 2 microns to about 40 microns. In still yet a further embodiment, the solids are comprised of talc. In another further embodiment, the carrier consists essentially of oils, vegetable oils, mineral oils, paraffin oils, esters, glycols, cellulose and olefins. In yet another further embodiment, the carrier comprises polypropylene glycol. The combination of hydrophobic talc and polypropylene glycol as an additive, functions as an excellent plugging agent. For purposes of this invention, the term xe2x80x9cplugging agentxe2x80x9d is defined as a solid having a particular size and shape so as to plug or seal off the surface micro-fractures of a porous sand, shale, or formation being drilled.
In still yet another embodiment, the solids comprises from about 2% to about 50% of the additive mixture of the present invention. In yet another further embodiment, the carrier comprises from about 50% to about 98% of the additive mixture. In still yet another embodiment, the beads comprises from about 2% to about 50% of the additive mixture.
In another embodiment, the present invention provides a method of improving the filter cake composition of a water-based drilling fluid, the method comprising: shearing colloidal solids with at least one carrier to create a suspended mixture to thereby allow the solids to be pre-wet with the carrier; admixing copolymer beads to the suspended mixture thereby allowing said beads to be pre-wet with the carrier; adding the suspended mixture to a water-based drilling fluid; and adding the additive to a well bore.
In yet another embodiment, the solids and the beads have an affinity for oils, esters, glycols and olefins. In still another embodiment, the beads have a specific gravity at from about 1.0 to about 1.5 and a size from about 40 microns to about 1500 microns, and the beads are comprised of styrene and divinylbenzene. In yet another embodiment, the solids have a size range from about 2 microns to about 40 microns. In still yet another embodiment, solids are comprised of talc. In a further embodiment, the carrier consists essentially of oils, hydrocarbon oils, vegetable oils, mineral oils, paraffin oils, esters, glycols and olefins. In still another further embodiment, the carrier comprises soybean oil. In a further embodiment, the talc of the present invention functions as a suspension agent and by making the talc oil wet, it becomes more hydrophobic and thus, more effective. In another further embodiment, the combination of talc and oil functions as an excellent plugging agent.
In another embodiment, the solids comprises from about 2% to about 50% of the additive mixture, the carrier comprises from about 50% to about 98% of the additive mixture, and the beads comprises from about 2% to about 50% of the additive mixture.